drivers/hwmon/sht21.c

   1 /* Sensirion SHT21 humidity and temperature sensor driver
   2  *
   3  * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
  18  *
  19  * Data sheet available (5/2010) at
  20  * http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/init.h>
  25 #include <linux/slab.h>
  26 #include <linux/i2c.h>
  27 #include <linux/hwmon.h>
  28 #include <linux/hwmon-sysfs.h>
  29 #include <linux/err.h>
  30 #include <linux/mutex.h>
  31 #include <linux/device.h>
  32
  33 /* I2C command bytes */
  34 #define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
  35 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
  36
  37 /**
  38  * struct sht21 - SHT21 device specific data
  39  * @hwmon_dev: device registered with hwmon
  40  * @lock: mutex to protect measurement values
  41  * @valid: only 0 before first measurement is taken
  42  * @last_update: time of last update (jiffies)
  43  * @temperature: cached temperature measurement value
  44  * @humidity: cached humidity measurement value
  45  */
  46 struct sht21 {
  47         struct device *hwmon_dev;
  48         struct mutex lock;
  49         char valid;
  50         unsigned long last_update;
  51         int temperature;
  52         int humidity;
  53 };
  54
  55 /**
  56  * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
  57  * milli celsius
  58  * @ticks: temperature ticks value received from sensor
  59  */
  60 static inline int sht21_temp_ticks_to_millicelsius(int ticks)
  61 {
  62         ticks &= ~0x0003; /* clear status bits */
  63         /*
  64          * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
  65          * optimized for integer fixed point (3 digits) arithmetic
  66          */
  67         return ((21965 * ticks) >> 13) - 46850;
  68 }
  69
  70 /**
  71  * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
  72  * one-thousandths of a percent relative humidity
  73  * @ticks: humidity ticks value received from sensor
  74  */
  75 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
  76 {
  77         ticks &= ~0x0003; /* clear status bits */
  78         /*
  79          * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
  80          * optimized for integer fixed point (3 digits) arithmetic
  81          */
  82         return ((15625 * ticks) >> 13) - 6000;
  83 }
  84
  85 /**
  86  * sht21_update_measurements() - get updated measurements from device
  87  * @client: I2C client device
  88  *
  89  * Returns 0 on success, else negative errno.
  90  */
  91 static int sht21_update_measurements(struct i2c_client *client)
  92 {
  93         int ret = 0;
  94         struct sht21 *sht21 = i2c_get_clientdata(client);
  95
  96         mutex_lock(&sht21->lock);
  97         /*
  98          * Data sheet 2.4:
  99          * SHT2x should not be active for more than 10% of the time - e.g.
 100          * maximum two measurements per second at 12bit accuracy shall be made.
 101          */
 102         if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
 103                 ret = i2c_smbus_read_word_swapped(client,
 104                                                   SHT21_TRIG_T_MEASUREMENT_HM);
 105                 if (ret < 0)
 106                         goto out;
 107                 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
 108                 ret = i2c_smbus_read_word_swapped(client,
 109                                                   SHT21_TRIG_RH_MEASUREMENT_HM);
 110                 if (ret < 0)
 111                         goto out;
 112                 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
 113                 sht21->last_update = jiffies;
 114                 sht21->valid = 1;
 115         }
 116 out:
 117         mutex_unlock(&sht21->lock);
 118
 119         return ret >= 0 ? 0 : ret;
 120 }
 121
 122 /**
 123  * sht21_show_temperature() - show temperature measurement value in sysfs
 124  * @dev: device
 125  * @attr: device attribute
 126  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 127  *
 128  * Will be called on read access to temp1_input sysfs attribute.
 129  * Returns number of bytes written into buffer, negative errno on error.
 130  */
 131 static ssize_t sht21_show_temperature(struct device *dev,
 132         struct device_attribute *attr,
 133         char *buf)
 134 {
 135         struct i2c_client *client = to_i2c_client(dev);
 136         struct sht21 *sht21 = i2c_get_clientdata(client);
 137         int ret = sht21_update_measurements(client);
 138         if (ret < 0)
 139                 return ret;
 140         return sprintf(buf, "%d\n", sht21->temperature);
 141 }
 142
 143 /**
 144  * sht21_show_humidity() - show humidity measurement value in sysfs
 145  * @dev: device
 146  * @attr: device attribute
 147  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 148  *
 149  * Will be called on read access to humidity1_input sysfs attribute.
 150  * Returns number of bytes written into buffer, negative errno on error.
 151  */
 152 static ssize_t sht21_show_humidity(struct device *dev,
 153         struct device_attribute *attr,
 154         char *buf)
 155 {
 156         struct i2c_client *client = to_i2c_client(dev);
 157         struct sht21 *sht21 = i2c_get_clientdata(client);
 158         int ret = sht21_update_measurements(client);
 159         if (ret < 0)
 160                 return ret;
 161         return sprintf(buf, "%d\n", sht21->humidity);
 162 }
 163
 164 /* sysfs attributes */
 165 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
 166         NULL, 0);
 167 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
 168         NULL, 0);
 169
 170 static struct attribute *sht21_attributes[] = {
 171         &sensor_dev_attr_temp1_input.dev_attr.attr,
 172         &sensor_dev_attr_humidity1_input.dev_attr.attr,
 173         NULL
 174 };
 175
 176 static const struct attribute_group sht21_attr_group = {
 177         .attrs = sht21_attributes,
 178 };
 179
 180 /**
 181  * sht21_probe() - probe device
 182  * @client: I2C client device
 183  * @id: device ID
 184  *
 185  * Called by the I2C core when an entry in the ID table matches a
 186  * device's name.
 187  * Returns 0 on success.
 188  */
 189 static int __devinit sht21_probe(struct i2c_client *client,
 190         const struct i2c_device_id *id)
 191 {
 192         struct sht21 *sht21;
 193         int err;
 194
 195         if (!i2c_check_functionality(client->adapter,
 196                                      I2C_FUNC_SMBUS_WORD_DATA)) {
 197                 dev_err(&client->dev,
 198                         "adapter does not support SMBus word transactions\n");
 199                 return -ENODEV;
 200         }
 201
 202         sht21 = kzalloc(sizeof(*sht21), GFP_KERNEL);
 203         if (!sht21) {
 204                 dev_dbg(&client->dev, "kzalloc failed\n");
 205                 return -ENOMEM;
 206         }
 207         i2c_set_clientdata(client, sht21);
 208
 209         mutex_init(&sht21->lock);
 210
 211         err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
 212         if (err) {
 213                 dev_dbg(&client->dev, "could not create sysfs files\n");
 214                 goto fail_free;
 215         }
 216         sht21->hwmon_dev = hwmon_device_register(&client->dev);
 217         if (IS_ERR(sht21->hwmon_dev)) {
 218                 dev_dbg(&client->dev, "unable to register hwmon device\n");
 219                 err = PTR_ERR(sht21->hwmon_dev);
 220                 goto fail_remove_sysfs;
 221         }
 222
 223         dev_info(&client->dev, "initialized\n");
 224
 225         return 0;
 226
 227 fail_remove_sysfs:
 228         sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 229 fail_free:
 230         kfree(sht21);
 231
 232         return err;
 233 }
 234
 235 /**
 236  * sht21_remove() - remove device
 237  * @client: I2C client device
 238  */
 239 static int __devexit sht21_remove(struct i2c_client *client)
 240 {
 241         struct sht21 *sht21 = i2c_get_clientdata(client);
 242
 243         hwmon_device_unregister(sht21->hwmon_dev);
 244         sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 245         kfree(sht21);
 246
 247         return 0;
 248 }
 249
 250 /* Device ID table */
 251 static const struct i2c_device_id sht21_id[] = {
 252         { "sht21", 0 },
 253         { }
 254 };
 255 MODULE_DEVICE_TABLE(i2c, sht21_id);
 256
 257 static struct i2c_driver sht21_driver = {
 258         .driver.name = "sht21",
 259         .probe       = sht21_probe,
 260         .remove      = __devexit_p(sht21_remove),
 261         .id_table    = sht21_id,
 262 };
 263
 264 /**
 265  * sht21_init() - initialize driver
 266  *
 267  * Called when kernel is booted or module is inserted.
 268  * Returns 0 on success.
 269  */
 270 static int __init sht21_init(void)
 271 {
 272         return i2c_add_driver(&sht21_driver);
 273 }
 274 module_init(sht21_init);
 275
 276 /**
 277  * sht21_init() - clean up driver
 278  *
 279  * Called when module is removed.
 280  */
 281 static void __exit sht21_exit(void)
 282 {
 283         i2c_del_driver(&sht21_driver);
 284 }
 285 module_exit(sht21_exit);
 286
 287 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
 288 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
 289 MODULE_LICENSE("GPL");